Volvo: please help with wiring, bulb failure, earth point

Question
90, 760 turbo wiring for trailer
I am installing trailer wiring on a 1990, 760 turbo sedan. I have what I have been told by several sites and trailer manufacturer is the proper wiring harness

I was given some help previously but need some clarification.

The harness that I have is a “modulite adapter trailer light power module, part #18193”

There are a total of 5 wires imputing this devise from vehicle:  

Red > battery
Green > right turn
Yellow > left turn
Brown > tail  
White > ground

output is 4 wires

Green > right turn
Yellow > left turn
Brown > tail  
White > ground

these output wires go to a, 3 female, one male pin plug

Green > right turn
Yellow > left turn
Brown > tail  
Are female inputs

White > ground :is male pin


This plug fits correctly and wires line up correctly with the corresponding plug that is wired into the trailer with the ground wire from the trailers plug going to white wire with a small metal clip




In the car right side lights have wires of the colors…

2 purp/wh , 4 n/a, 6 thick blk , 8 rd/yl 1 yl/wh, 3 blk/gry 5 blue/gr 7 yl/wh
Best guess 5 blue /green

on the left side wire colores are

2 r/y , 4na, 6 thick blk , 8 purp/wh , 1 r/w, 3 green, 5blk/gry ,7 r/w
Best guess 3 green

And I have a good power wire off the battery

Here is the info I got last time  posted:

“Ground is Earth or the metal bodywork of the car. Usually Black is the colour for this and goes to an earth point. Left turn is Green, Right turn is Blue/Green, rear fogs are Violet(Purple)/White (both sides), Brake lights are both Yellow/Red, but you need to take the supply (one wire only) from the other side of the rear bulb failure warning unit (grey box on side wall of left rear wing) which is the Yellow wire coming into the unit. The rear tails are similar in that they also have to be fed from the other side of the same unit. Left tail feed is the White wire coming into the unit and right tail feed is the Green wire coming into the unit. Doing this avoids making the bulb failure indicator lamp illuminate when the caravan or trailer is connected.”

I guess my question is ..because this trailer light power module only has one tail wire feed coming in and going out  (by the way the labels on power module say right turn/stop and left turn/stop above where the output turn signal wires comes out of unit but only, right turn, left turn above where the turn signal wires enter the unit) where and what color is this wire in the car? What about brakes?

I have had limited success without the power module ,wiring directly from behind and under light fixtures wiring into a basic, white, green. Yellow, brown wired plug that fits the trailer plug  

blue green to green right turn
green to yellow left turn
red/white to brown
and white ground from car

  I get tail light, turns signal, but no brakes on trailer this way and the light bulbs seem a bit dim.

Also there is a wire tapped from the yellow/red brake on the left side below light fixture that is brake light, I tried putting this with the tail light red/white to brown and got nothing but a weaker light on trailer going out when brakes applied, when I replaced the red/ white to brown tail input wire with this one tapped off the yellow/red brake I had a weak brake signal at light but of course no always on tail light

Any ideas on how to get this system working properly with good tail, turn, and brake lights

THANKS! William


Answer
Hello WIlliam! You will need to get a wiring diagram for your year and model car. Go to www.volvotechinfo.com for a manual. Or, using a test light, have someone operate all lights while probing with the light. I'm sorry I don't know the wiring colors off the top of my head.


Jimmy